Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight-cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand or DOD. Operation of the engine using all of the engine cylinders is referred to as an activated mode. A deactivated mode, in contrast, refers to operation using less than all of the cylinders of the engine (i.e., one or more cylinders not active).
In the deactivated mode, there are less cylinders operating. As a result, there is less drive torque available to drive the vehicle driveline and accessories, such as an alternator, a coolant pump or an air conditioning compressor. Engine efficiency, however, is increased because of decreased fuel consumption (i.e., no fuel supplied to the deactivated cylinders) and decreased engine pumping. Because the deactivated cylinders do not take in and compress fresh intake air, pumping losses are reduced.
Movement between the activated mode and the deactivated mode has the potential to increase noise, vibration and harshness in the engine, which may be transmitted to the driver. In addition, conventional DOD systems move between a full array of cylinders and half of the cylinders. For example, an eight-cylinder engine can operate with all eight cylinders in the activated mode and then reduce to four cylinders in the deactivated mode. The addition or subtraction of torque due to the activation or deactivation of multiple cylinders at a time can increase noise, vibration and harshness.